In cake decorating, after a uniform layer of icing is applied, the cake is often trimmed with strings of icing applied by means of an extruder. The extruder can be in the form of a flexible bag having an attached nozzle though which icing in the bag is forced by manual squeezing of the bag. Other common forms of extruders include an extruder comprising a cylindrical chamber, an outlet nozzle through which icing flows from the interior of the cylindrical chamber, and a plunger, movable axially in the chamber, for applying pressure to the icing and thereby extruding the icing through the nozzle. In some extruders, the plunger is operated manually. In others, the plunger is motor-driven. The nozzles can have apertures configured to produce strings of icing of various sizes and cross-sectional shapes. For example, the nozzle aperture can be designed to extrude a string of icing in the form of a flat ribbon, or one having a star-shaped cross-section.
Extruders have also been designed with rotating nozzles for producing twisted strings of icing. For example United States Patent Publication 2008/0089967, published Apr. 17, 2008, describes a piping bag having a rotatable nozzle. Other extruders have been devised for dispensing icing through plural adjacent nozzles that can rotate about a central axis to produce a rope-like string of icing. Examples of such extruders are described in U.S. Pat. Nos. 7,713,585, granted May 21, 1929, 5,492,706, granted Feb. 20, 1996, and 5,603,965, granted Feb. 18, 1997. Despite the developments exemplified by the above-mentioned patents and patent publication, a need remains for a simple and easy-to-use extruder capable of delivering a twisted string of icing of uniform quality, consisting of a single strand delivered through a single nozzle, or plural strands delivered through two or more nozzles and twisted about one another.